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diff --git a/src/collections/mod.rs b/src/collections/mod.rs
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+//! Parallel iterator types for [standard collections][std::collections]
+//!
+//! You will rarely need to interact with this module directly unless you need
+//! to name one of the iterator types.
+//!
+//! [std::collections]: https://doc.rust-lang.org/stable/std/collections/
+
+/// Convert an iterable collection into a parallel iterator by first
+/// collecting into a temporary `Vec`, then iterating that.
+macro_rules! into_par_vec {
+    ($t:ty => $iter:ident<$($i:tt),*>, impl $($args:tt)*) => {
+        impl $($args)* IntoParallelIterator for $t {
+            type Item = <$t as IntoIterator>::Item;
+            type Iter = $iter<$($i),*>;
+
+            fn into_par_iter(self) -> Self::Iter {
+                use std::iter::FromIterator;
+                $iter { inner: Vec::from_iter(self).into_par_iter() }
+            }
+        }
+    };
+}
+
+pub mod binary_heap;
+pub mod btree_map;
+pub mod btree_set;
+pub mod hash_map;
+pub mod hash_set;
+pub mod linked_list;
+pub mod vec_deque;
+
+use self::drain_guard::DrainGuard;
+
+mod drain_guard {
+    use crate::iter::ParallelDrainRange;
+    use std::mem;
+    use std::ops::RangeBounds;
+
+    /// A proxy for draining a collection by converting to a `Vec` and back.
+    ///
+    /// This is used for draining `BinaryHeap` and `VecDeque`, which both have
+    /// zero-allocation conversions to/from `Vec`, though not zero-cost:
+    /// - `BinaryHeap` will heapify from `Vec`, but at least that will be empty.
+    /// - `VecDeque` has to shift items to offset 0 when converting to `Vec`.
+    #[allow(missing_debug_implementations)]
+    pub(super) struct DrainGuard<'a, T, C: From<Vec<T>>> {
+        collection: &'a mut C,
+        vec: Vec<T>,
+    }
+
+    impl<'a, T, C> DrainGuard<'a, T, C>
+    where
+        C: Default + From<Vec<T>>,
+        Vec<T>: From<C>,
+    {
+        pub(super) fn new(collection: &'a mut C) -> Self {
+            Self {
+                // Temporarily steal the inner `Vec` so we can drain in place.
+                vec: Vec::from(mem::replace(collection, C::default())),
+                collection,
+            }
+        }
+    }
+
+    impl<'a, T, C: From<Vec<T>>> Drop for DrainGuard<'a, T, C> {
+        fn drop(&mut self) {
+            // Restore the collection from the `Vec` with its original capacity.
+            *self.collection = C::from(mem::replace(&mut self.vec, Vec::new()));
+        }
+    }
+
+    impl<'a, T, C> ParallelDrainRange<usize> for &'a mut DrainGuard<'_, T, C>
+    where
+        T: Send,
+        C: From<Vec<T>>,
+    {
+        type Iter = crate::vec::Drain<'a, T>;
+        type Item = T;
+
+        fn par_drain<R: RangeBounds<usize>>(self, range: R) -> Self::Iter {
+            self.vec.par_drain(range)
+        }
+    }
+}